A Study of Low Speed Preignition Mechanism in Highly Boosted SI Gasoline Engines

摘要

The authors investigated the reasons of how a preignition occurs in a highly boosted gasoline engine. Based on the authors' experimental results, theoretical investigations on the processes of how a particle of oil or solid comes out into the cylinder and how a preignition occurs from the particle. As a result, many factors, such as the in-cylinder temperature, the pressure, the equivalence ratio and the component of additives in the lubricating oil were found to affect the processes. Especially, CaCO_3 included in an oil as an additive may be changed to CaO by heating during the expansion and exhaust strokes. Thereafter, CaO will be converted into CaCO_3 again by absorbing CO_2 during the intake and compression strokes. As this change is an exothermic reaction, the temperature of CaCO_3 particle increases over 1000K of the chemical equilibrium temperature determined by the CO_2 partial pressure. The possibility of a preignition due to particles including CaCO_3 particles is numerically simulated comparing with the experimental results.